1. Field of the Invention
The present invention relates to a photo-curable silicone composition which is hardened by being subjected to visible light radiation, and more particularly to a photo-curable silicone composition and an adhesive composition having prominent properties such as resistance to heat, cold and climatic conditions which are peculiar to silicone rubber, and which are set by means of visible light radiation, thereby contributing to the improvement of productivity and energy savings at the photo-setting step, accordingly.
2. Description of the Prior Art
Photo-curable silicone materials, in general, are advantageous in having being resistant to heat and humidity, have excellent electrical properties in comparison with other organic materials, and can be controlled to form various states such as gels, rubbers and resins. Therefore, they are widely utilized in a variety of commercial applications, for example, as coating and covering materials and adhesives for plastic substrates of low heat-resistance and for heat-sensitive electric and electronic parts. For this reason, numerous photo-curable silicone compositions and photo-curable silicone adhesives are suggested for the purpose of improving productivity and saving energy.
For example, U.S. Pat. No. 3,726,710 by Berger et al. discloses silicone compositions comprising a vinyl-radical-containing organopolysiloxane compound and various photoreaction initiators, which are set by means of high intensity ultraviolet light radiation. These silicone compositions, however, can be cured only by ultraviolet light having a wavelength shorter than 300 nm, and they cannot be cured, accordingly, by radiation having a wavelength longer than 300 nm. Therefore, these silicone compositions have a defect in that, in curing, the utilization of light energy is low, thus requiring the photo-setting machine to be used at high power.
As another prior art reference, U.S. Pat. No. 3,816,282 by Viventi discloses silicone compositions comprising a mercapto-radical-containing organopolysiloxane, polymethylvinylsiloxane and various organic peroxides. However, these silicone compositions must also be cured by radiation only in the ultraviolet range. Consequently, these silicone compositions have the same defect as described above.
In addition to the two U.S. patents above, U.S. Pat. No. 4,364,809 by Satoh et al. discloses a silicone composition comprising a vinyl-radical-containing organopolysiloxane and an organic peroxide. However, this silicone composition also cannot be cured by radiation outside the ultraviolet range, and thereby gives rise to the same defect found for the silicone compositions described above.
U.S. Pat. No. 4,908,395 by the applicant of the present invention suggests a silicone composition comprising a vinyl-radical-containing organopolysiloxane, an aromatic ketone photo-reaction initiator and a trialkenyl isocyanurate. However, as was found for the above compositions, this silicone composition cannot be cured by any radiation lying outside the ultraviolet range, and therefore has the same defect inherent in the compositions described above.